A space link allows several terrestrial stations to communicate with one another, via a satellite, once these stations are situated in the geographical zone (or coverage) delimited by one of the satellite's spots, as shown by FIG. 1. The presence of interference within or outside the coverages may prevent any communication between the stations. The robustness of the links to the presence of interference requires that the links be protected against such interference.
A first protection with regard to interference can be envisaged by implementing a method of frequency evasion (FE) which consists in emitting the information on frequencies which change regularly every T seconds where T is called the duration of the time slot. The frequency change law, called the frequency-hopping law, is generally periodic of long period, thereby rendering it random on a fairly short observation scale. It is known to the satellite and to all the useful stations. It allows the link not to remain for more than T seconds on a channel with interference and to benefit from undisturbed channels if the latter exist.
Although it is effective, this technique, which is aimed at eluding interference rather than rejecting it, is limited in the case of strong interference spread over a very wide band and entailing the pollution of a significant fraction of the number of time slots. For these critical situations, an anti-interference fighting system based on antenna processing is generally added to the FE.
Anti-interference fighting based on antenna processing currently constitutes an effective way of protecting one or more space communications with regard to interference. Anti-interference fighting based on antenna processing consists in implementing an antenna termed adaptive on reception, possessing the capability of adapting its radiation pattern in real time to the signals received by constructing pattern voids in the direction and at the frequency of the interference while preserving a sufficient gain in the direction of the link or links to be protected, as illustrated by FIG. 2. This result can be obtained on the basis of a minimum of information on the links to be protected such as the knowledge of the position of the useful stations, of their band, of the theatre of operation or else of training sequences conveyed by the stations, without a priori knowledge on the interference present.
A certain number of antenna processing systems have been developed for protecting FE links from interference [1] [2]. Nevertheless, most of these systems implement a set of weightings per station [1], which turns out to be very expensive or require the duplication of the reception chains [2].